What are fuel cells?
Fuel cells convert fuel and air directly to electricity, heat and water in an electrochemical process. Unlike conventional engines, they do not burn the fuel and run pistons or shafts, and so have fewer efficiency losses, low emissions and no moving parts.
What are the different types of fuel cells?
- There are several different types of fuel cells but they are all based around a central design, which consists of two electrodes (electrical conductors), a negative anode and a positive cathode. These are separated by a solid or liquid electrolyte that carries electrically charged particles between the two electrodes. A catalyst, such as platinum, is often used to speed up the reactions at the electrodes.
- Fuel cells are classified according to the nature of the electrolyte and their operating temperature. Each type requires particular materials and fuels and is suitable for different applications. Namely,
|Proton Exchange Membrane (PEMFC)||80-100|
|Direct methanol fuel cell (DMFC)||90|
|Phosphoric acid (PAFC)||140|
|Molten carbonate (MCFC)||800|
|Solid oxide (SOFC||800-1000|
|Regenerative fuel cell||-|
What is the principle on which fuel cells operate?
- A fuel cell consists of an electrolyte sandwiched between two electrodes. Oxygen passes over one electrode and hydrogen over the other, generating electricity, water and heat.
- A fuel cell system that includes a "fuel reformer" can use the hydrogen from any hydrocarbon fuel. On the other hand, high temperature fuel cells do not need a fuel reformer and can directly use fossil fuels such as natural gas, coal gas, etc. Since the fuel cell relies on chemistry and not combustion, emissions from this type of system are still much smaller than emissions from the cleanest fuel combustion processes.
What are the current uses of fuel cell technology?
Currently, the cost of fuel cells is too high for them to be put in general use. Ongoing research aims to reduce the cost and thus increase demand.
Overview of the technology
- A fuel cell is an electro-chemical energy converter. At the simplest conceptual level it combines hydrogen with oxygen to produce water and electricity. As it is essentially an electro-chemical device, it functions rather like a battery but, unlike a battery, it doesn't store the energy itself. It is a flow process which draws liquid or gaseous fuel from a separate tank and if necessary converts it to hydrogen in a reformer. The hydrogen is then combined with oxygen from air in the fuel cell to produce water and electricity. The energy conversion process in the fuel cell is therefore intrinsically clean and silent.
- A fuel cell generally uses hydrogen as a fuel but other fuels such as natural gas, methanol and even coal can also be used. However, in most fuel cell types these fuels must first be transformed into hydrogen by means of a reformer or a coal gasifier. The direct outputs from fuel cells are electrical power and heat. Depending on the fuel cell type, it is possible to deliver electricity and heat from 80°C to 800°C.
What are the various aspects of the technology and its applications?
The central working part of a Proton Exchange Membrane (PEM) fuel cell is the membrane electrode assembly, which is a layered structure consisting of an anode, polymer electrolyte membrane and cathode. Hydrogen gas is fed to the anode and diffuses through it to a thin platinum catalyst layer at the boundary between the anode and polymer membrane. Here the hydrogen is converted into protons and electrons. At the cathode, the protons and electrons come together again and combine with oxygen from air to form water, which is carried away. Heat is generated in the process.